1. Field of the Invention
The present invention relates to a split nut opening/closing device for tie bar, which is applied to a mold clamping apparatus for an injection molding machine, a pressing machine, or the like. More particularly, it relates to an electric split nut opening/closing device in a mold clamping apparatus, which has a simple construction and high response.
2. Description of Related Art
Conventionally, in the mold clamping apparatus for an injection molding machine, a movable platen is brought closer to a fixed platen generally fixed to an apparatus base by using a cylinder with a small diameter and a large stroke, and thereby molds attached to the movable and fixed platens are brought into contact with each other, by which mold closing is performed. At this time, a two-piece nut (split nut) is engaged with and connected to a threaded portion at the tip end of each of four tie bars that are fixed to one platen and project from the other platen, by which a mold clamping force is generated by giving tension to the tie bar using a large-diameter and small-stroke cylinder. As an opening/closing device for this split nut, various types of devices have so far been proposed.
First Conventional Example
A xe2x80x9cmold clamping split nut opening/closing devicexe2x80x9d (Unexamined Japanese Utility Model Publication No. 4-87218) of a type such that a split nut is opened and closed horizontally using an electric motor will be described as a first conventional example with reference to FIGS. 9 and 10.
As shown in FIG. 9, this split nut 1 consists of a pair of, left and right, half pieces A and B. A slide box 4 is disposed in an upper space between the half pieces A and B, and two guide rods 5 are inserted in the side portions of the half pieces A and B and the slide box 4. In the lower part, one guide rod 5 is inserted in the half pieces A and B. Both ends of each of these guide rods 5 are fixed to the half piece A and a plate 7. The half piece B and the slide box 4 are slidable via bushes 15 and 16, respectively. The slide box 4 is slidably supported by a guide stand 3 projecting from a position just over a tie bar 2 of a fixed platen (not shown), and is configured so as to be movable in the axial direction (direction perpendicular to the paper in FIG. 9) of the tie bar 2.
The plate 7 is fitted with an electric motor 23 via a bracket 21. To an output shaft 22 of the electric motor 23, a ball screw 20 is connected via a coupling 35. Also, the ball screw 20 is inserted in a hole 36 in the half piece B and a hole 37 in the plate 7, and is engaged with a ball nut 19. The ball nut 19 is fixed to the half piece B via an adapter plate 27, thus forming opening/closing drive means for the split nut 1.
Also, on the bottom surface of the slide box 4 is protrusively provided a support pin 10, and on the top surfaces of the left and right half pieces A and B are protrusively provided pins, 12a and 12b, respectively. As shown in FIG. 10, the support pin 10 is inserted in a round hole in the center of a link plate 11, and pins 12a and 12b are inserted in elongated holes at both ends thereof.
Reference numeral 25 denotes a slit plate fixed to the coupling 35, and 26 denotes a pulse sensor fixed to the bracket 21. By these elements, the rotation of the ball screw 20 is counted to find the position of the half piece B.
In order to close the split nut 1 in the open state in which the half pieces A and B are separated, the electric motor 23 is rotated in the direction such that the ball nut 19 is moved away. The half piece B is moved in the direction such as to come closer to the half piece A, and the pin 12b turns the link plate 11 around the support pin 10 in the closing direction (counterclockwise direction in FIG. 10). At this time, the link plate 11 turning in the closing direction moves the half piece A in the closing direction (right direction in FIG. 10) via the pin 12a. Thus, the half pieces A and B move while always maintaining the symmetrical position with respect to the tie bar 2 lying in the same position as the support pin 10.
Inversely, in order to open the closed split nut 1, the above-described operation has only to be performed entirely reversely, so that the explanation thereof is omitted.
The engagement phase of the threaded portion of the split nut 1 with the tie bar 2 is adjusted by an engagement adjusting device, not shown.
Second Conventional Example
Although the above-described split nut opening/closing device is provided on each of four tie bars in the first conventional example, a split nut opening/closing device for opening and closing two split nuts by one cylinder has been proposed as a closing device in a xe2x80x9cmold fixing device of injection and compression molding machinesxe2x80x9d (Japanese Patent Publication No. 37-8490). This device will be described as a second conventional example.
FIG. 11 shows an opening/closing device (closing device) 50. In FIG. 11, reference numeral 51 denotes a movable platen (movable attachment plate), 52 denotes a tie bar (transverse rod), 53 denotes a cylinder, 54 denotes two pistons in the cylinder 53, 55 denotes two rods (piston rods), 56 denotes a conduit tube. The rod 55 is connected to one end of a link plate (bent rod) 57, and the other end of the link plate 57 holds one end of a half piece 58 of a split nut (holding member). The other end of the half piece 58 is rotatably supported by a pin (shank) 59 provided on the movable platen 51.
When a pressure oil is supplied from the conduit tube 56 to two oil chambers 53a on both sides of the cylinder 53, the rod 55 decreases its stroke, so that the link plate 57 turns so as to be horizontal, increasing the transverse length. The half piece 58 is turned around the pin 59 to be opened, by which the connection with the tie bar 52 is released. Also, when the pressure oil is inversely supplied to an oil chamber 53b on the center of the cylinder 53, the rod 55 increases its stroke, so that the link plate 57 turns so as to form an angle with respect to the horizon, whereby the half piece 58 is turned and closed.
In this device, which of the two rods 55 and the half piece 58 moves earlier cannot be determined unequivocally.
The opening/closing device of the first conventional example is of a type such that the electric motor 23 is driven to linearly move the half pieces A and B, by which the split nut is opened and closed to the right and left. Therefore, the opening/closing device of this type has an advantage of high response, but has a disadvantage of complicated construction because the opening/closing device is provided on each of the four tie bars 2.
The opening/closing device of the second conventional example is of a type such that one cylinder 53 is used for two upper and lower tie bars 52 to rotationally move the half pieces 58 on the circumference, by which the split nut is opened and closed to the right and left. Therefore, the opening/closing device of this type has an advantage of simple construction of device because two split nuts are opened and closed by one cylinder 53, but has disadvantages of low response because of the use of the cylinder 53 and less unequivocalness of the motion of the rod 55 of the cylinder 53 and the half piece 58.
An object of the present invention is to provide an electric split nut opening/closing device in a mold clamping apparatus, in which an electric motor is driven to linearly move a half piece while unequivocally restraining the motion, by which two right and left tie bars are opened and closed at the same time by one device.
To solve the above problems, the present invention provides solving means by using the configurations described below.
The present invention provides an electric split nut opening/closing device in a mold clamping apparatus in which a fixed platen for holding a fixed mold and a movable platen for holding a movable mold are provided, and a tip-end threaded portion of a tie bar, one end of which is fixed to either one of the platens and the other end of which is projected by penetrating the other platen, is engaged with a split nut provided on the other platen to connect the fixed platen to the movable platen, by which a mold clamping force is generated between the platens by giving tension to the tie bar, wherein a pair of left half piece and right half piece of the split nut are slidably supported so as to hold the tie bar therebetween, and the left half piece and right half piece of the two sets of split nuts are brought into contact with and separated from each other at the same time by common driving means so as to hold the tie bar.
Also, in the present invention, one of the half pieces constituting the split nut is driven by a reciprocating device driven by a motor; the movement of the one half piece is transmitted to the other half piece via a link mechanism; and the other half piece is brought into contact with and separated from one half piece in connection with one half piece.
Further, in the present invention, a guide box is provided in positions of two tie bars on the other platen; the guide box slidably support the paired left half piece and right half piece of the left and right split nuts so as to hold the tie bar; the guide box is provided with a link plate rotatably supported via a support pin; a pin engaging with an elongated hole formed at both ends of the link plate is provided on each of the left half piece and right half piece; and the left half piece and right half piece are link connected in a restrained manner so as to move symmetrically with respect to the support pin.
Still further, in the present invention, two connecting rods penetrate the two sets of left half piece and right half piece; one end of the connecting rod is fixed to one half piece, and the other half piece is slidably supported; a geared motor with brake is mounted on a plate fixed to the connecting rod; and the left half piece and right half piece of one split nut are brought closer to and separated from each other via a reciprocating mechanism provided on an output shaft of the geared motor with brake.
Also, in the present invention, the left half piece and right half piece of one split nut are brought closer to and separated from each other by a reciprocating device consisting of a ball shaft connected to the output shaft of the geared motor via a coupling and a ball nut which engages with the ball shaft and is connected to the right half piece of one split nut.
Further, in the present invention, the guide box is made up of attachment portions attached to a side portion and a front portion of the platen, two bottom plates for supporting the half pieces of the split nut, and a groove portion provided between the bottom plates.
The present invention can use a rotating crank mechanism in place of the aforementioned reciprocating device.
Specifically, the present invention can be configured so that the left half piece and right half piece of one split nut are brought closer to and separated from each other by a driving device comprising a geared motor with brake whose output shaft is installed to a bracket fixed to the connecting rod so as to be perpendicular to the connecting rod; a crank arm which is fixed to the output shaft of the geared motor with brake and has a pin at the tip end; a joint member which is installed to the right half piece of one split nut via an adapter member and is given an initial compressive force by spring means; and a connecting link one end of which is rotatably connected to the tip-end pin of the crank arm and the other end of which is rotatably connected to the joint member via a pin.
Further, the present invention can be configured so that the tip-end pin of the crank arm is supported at both ends, and the connecting link has a curved shape so as to avoid the interference with the crank arm.